1. Field of the Invention
The present invention relates to a power tilt apparatus preferably used in a snowplow, ship propulsion machinery and the like.
2. Description of the Related Art
In the conventional snow plow and ship propulsion machinery, as described in Japanese Patent Application Laid-Open No. H7-228297 (patent document 1), a power tilt apparatus is disclosed in which an operation state of a cylinder apparatus is switched between an extension side and a compression side by a switching valve apparatus provided in a pipe passage connecting the cylinder apparatus and the pump apparatus, in accordance with an oil feeding direction of a pump apparatus.
In the conventional power tilt apparatus, a valve apparatus such as the switching valve apparatus, a manual valve apparatus or the like, a plug and the like provided in the pipe passage would be fixed so as to be screwed into a hole provided in a valve block. In a bored portion or a threaded portion of the valve block, foreign particles such as burrs or the like can not be completely removed by a washing process after the working process, so that the foreign particles occasionally are generated during screwing of the valve apparatus or the like. If the foreign particles are in the middle of the pipe passage, a malfunction of the valve apparatus is caused. In particular, in a compact valve apparatus, the possibility of malfunction is relatively high.
Accordingly, in the conventional power tilt apparatus, the pump apparatus is provided with a filter such as a mesh filter or the like.
The prior art has the following problems.
(1) Even in the case that the pump apparatus is provided with the filter, foreign particles are generated in the middle of the pipe passage and are caught on the filter only after they reach the tank. They are caught on the valve apparatus in the process of reaching the tank, and the malfunction is caused, particularly in the compact valve apparatus.
(2) In the case of the mesh filter, a frame for supporting the mesh is necessary, and an unintended disassembly prevention is also necessary. If the filter is downsized, an opening area of the filter is reduced by the frame or the like, and the filter is resultantly poor in strength and/or flow capacity. Accordingly, this structure is not adequate for a high pressure portion or a portion having a large flow rate.